Hydraulic servo-valve



Feb. 25, 1958 M. l. PLACE HYDRAULIC SERVO-VALVE 2 Sheets-Sheet 1 Filed April 19, 1955 Fig.|.

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ATTORNEY M. I. PLACE HYDRAULIC SERVO-VALVE Feb 25, 1958 2 Sheets-Sheet 2 Filed April 19, 1955 United States Patent HYDRAULIC SERVO-VALVE Application April 19, 1955, Serial No. 502,471

Claims. (Cl. 137-623) This invention relates to hydraulic servo-valves, and more particularly to servo-valves wherein hydraulic flow of large magnitude is adapted to be controlled by relatively low power electrical signals.

Hydraulic servo-valves of the type here under consideration generally comprise a valve having a pressure port connected to a source of hydraulic pressure, two ports connected to opposite sides of a piston or a similar work device, and at least one drain port connected to a sump or other accumulator associated with the fluid flow pressure source. Electro-hydraulic servo systems by D. G. OBrien and R. D. Atchley appearing in Electrical Manufacturing of April, 1954, pages 8996. A movable valve element, or spool, within the valve chamber gates the flow of hydraulic fluid from the pressure port to one or the other of the work ports and from the work port to which fluid pressure is not applied to one of the drain ports. The work port to which the hydraulic pressure port is coupled is determined by moving the spool in one direction or the other from a given central position. At page 95 of the aforementioned article, there is described a servovalve, the movement of the spool of which is controlled by metering the flow of fluid from a chamber associated with one end of the spool. The fluid pressure in the chamber is balanced by a spring which exerts biasing pressure against the opposite end of the spool. The fluid flow from the chamber is controlled by a spring biased flapper valve, the relative position of which with respect to'an orifice opening into the chamber is controlled by electromagnetic means associated therewith.

This servo-valve in common with like devices known Such devices are described in the article to the art is subject to clogging of the hydraulic nozzle which controls the position of the valve spool from dirt and other foreign matter, which almost inevitably finds its way into a hydraulic system and which is quite diflicult to effectively remove. Furthermore, the relatively slow response of prior art valves has become an increasingly important shortcoming thereof, particularly in connection with the control of guided missiles and like high Another object is to provide a hydraulic servo-valve having an improved frequency response characteristic.

. Still another object is to provide a hydraulic servovalve, the operating characteristics of which are such that theneed for an external source of effectively eliminated.

dither control is 2,824,574 C6 Patented Feb. 25, 1958 Still another object is to provide a hydraulic servo-valve that is relatively simple to construct and to service.

Other objects and features will become apparent from consideration of the following description of my invention when taken with reference to the accompanying drawings, wherein:

Figure 1 is a sectional view of a preferred embodiment of my invention;

Fig. 2 is a top sectional view taken along the line H- H of Fig. 1;

Fig. 3 is a partial end sectional view taken along the line IIIIII of Fig. 2; and

Fig. 4 is a partial sectional view of a modification of my invention.

With reference now to the figures of the drawings generally, and particularly to Fig. 1, there is shown a valve block 1 which is preferably of aluminum or similar nonmagnetic material which may be either circular or rectangular in cross section as may be convenient; the rec tangular configuration shown in the drawings is preferred. A longitudinal bore 2 is provided within block 1 into which opens load ports 3a and 3b and pressure port 33 (see Fig. 3). Pressure port 33 is drilled into the block between the load ports. An additional opening adapted to receive actuator is provided which opens into the longitudinal bore 2 approximately midway between the ends thereof. The longitudinal bore 2 is preferably of circular cross section for ease in assembling the component parts to be described.

Proceeding from the center of the longitudinal bore 2 and progressing towards the ends thereof, there are assembled in juxtaposition the following component parts: valve guides 5a and 5b, spiders 10a and 10b, valve guides 16a and 16b, spiders 11a and 11b, valve guides 21a and 21b, end guides 17a and 17b, and circular plates 19a and 19b. The valve guides 5a and 5b in combination with the interior of valve block 1 form a central cavity 9 into which pressure port 33 opens. The valve guides 5a and 5b are notched so as to receive O-rings 65a and 65b which provide a fluid tight seal for the central cavity.

The valve guides and spiders are provided with central bores of the same cross section so as to receive valve spools 6a and 6b in sliding fit therewith. Each valve spool is provided with a pair of annular collars 24a, 24b and 13a, 13b which are the parts adapted to be in sliding fit with the interior of the valve guides as noted above. Alternatively, the spool may be machined so that the collars are merely enlarged sections thereof.

Each valve spool is additionally provided with a central bore, denoted (in and 3b, which extends longitudinally therethrough and which narrows to a nozzle denoted 7a and 7b at the ends thereof, which nozzles open into a central cavity 9. Orifices 12a and 1222 are provided which provide restricted fluid communication between the central bore 8a, 8b and the portions of the valve spools between the annular collars.

Valve guides 21a and 21b and the valve block are machined to provide cavities 29a and 2911 which are in fluid communication with drain port 35 by means of longitudinal bore 43. Valve guides 21a and 21.12 are additionally drilled so as to provide channels 51a, 5112, the cavities 29a, 29b and the section of the valve spool between the annular collars. Annular collars 16a and 16b have longitudinal dimensions such that they extend between the opposing faces of valve guides 5a and 5b so as to prevent fluid communication between work ports 3a, 3b and the central cavity 9 and between work ports 3a, 3b and the' drain port cavities 2%, 2% when the valve spools are centrally positioned. The work ports 3a, 3b are adapted to be in fluid communication with the central cavity and the drain cavities through radial slots in the spiders 10a, 10b and 11a, 11b.

End plates a, 15b of the valve spools are respectively adapted to slide within the central bore through end guides 17a and 17b, for the purpose of limiting the inward movement of the spools toward the central pressurized cavity. Threaded adjusting screws 25a, 25b which are adapted to thread through end caps 23a, 23b bear against circular plates 19a, 19b so as to bring the various valve guides and the other stationary parts associated therewith (thus excluding the movable valve spool) into abutting relationship.

The pressure port 33 and the drain port 35 are respectively adapted to be connected to a source of fluid pressure and an accumulator associated therewith; the work ports 3a and 3b are adapted to receive fluid conduits which connect to the opposite faces of a hydraulic piston or other work device such as shown in the art by OBrien and Atchley, referenced above.

The actuator for the servo-valve comprises an armature 109 having a reduced end section 121 which is inserted between the ends of spools 6a and 6b at which orifices 7a and 7b open, a flanged tube 117 which is in tight fit with the port 118 opening into the central cavity 9, two pole pieces 103, 105 on opposite sides of flanged tube 117, a coil 125 wound on coil form 123 with the pole pieces 103, 105 so as to form an electromagnet, two permanet magnets 39 and 41, and an O-ring 119 for pro viding a fluid-tight seal between valve block 1 and flanged tube 117. The armature 109, which is made of iron or similar ferromagnetic material, has a reduced neck 113 which acts as a centering spring therefor, and an enlarged section 111 which wedges into the interior of flanged tube 117.

The primary function of the flanged tube is to seal off hydraulic fluid from the coil and lead wires of the electromagnet. The flanged tube also serves as a convenient mounting base for the armature without the need for additional hardware or fasteners and can additionally be used as a jig to locate the two pole pieces 103, 105 during assembly. It is essential that the tube be fabricated from a non-magnetic material such as a non magnetic stainless steel.

A pair of permanent magnets 39, 41 are mounted in parallel on the pole pieces so that the permanent magnet flux resulting therefrom divides equally across the tube between the air gaps of the pole pieces. The armature is, therefore, deflected in one direction or the other in accordance with the direction of current through the coil 125, inasmuch as the flux distribution across the lower air gap will be such as to produce a considerable deflecting torque on the armature. The resultant force on the armature is proportional to the product of the permanent magnet flux and the flux induced in the armature by the electromagnet.

The operation of the servo-valve is as follows. Assume that the armature 109 is centrally positioned (no current flowing through coil 125) and that ports 33 and 35 have been respectively connected to a suitable source of fluid pressure and to a drain accumulator. The pressure acting over the inner areas of the spool fronting on cavity 9 will tend to drive the spools outwardly, allowing fluid flow through orifices 7a and 7b. When pressure has been built up in the two compartments formed by end plates 19a, 19b, end guides 17a and 17b and butt plates 15a, 15b by flow entering orifices 7a, 7b and being metered out fixed orifices 12a, 12b until the pressure on the bottom of the spools equals the pressure exerted against the spools at the ends facing armature 10?, the spool will float at a fixed distance from the armature. Fluid flow will continue through the gaps 31a, 31b between armature 109 and the respective spools, through the central bores 8a, 8b and out the orifices 12a, 12b to the drain cavities 29a, 29b and the drain port 35.

Considering the operation of valve spool 6a alone as exemplary of the operation of both spools, moving the armature away from the spool will increase gap 31a,

allowing more flow through central bore 8a and increasing the pressure on the right hand side of the spool, thus driving the spool toward the armature until balance is again achieved. Moving the armature toward the spool decreases the amount of flow through the gap 31a, thereby decreasing the pressure on the right-hand side of the spool as fluid is meteredout through orifice 12a and driving the spool toward the right until pressure balance is again achieved. Thus, the spool tends to seek a null position at a given distance away from the armature depending upon the fluid pressure within cavity 9.

Thus, both spools may readily be moved from the right end to the left depending upon the deflection of armature 109. Moving armature 109 to the right will move both valve spools 6a and 6b to the right; this will provide fluid communication between pressure port 33 and work port 3a and between work port 3b and drain port 35, thereby exerting differential pressure on the piston or other work device connected to the work ports. Similarly, moving the armature to the left will move the spools to the left and provide fluid communication between pressure port 33 and work port 3b, and between work port 3a and drain port 35, thus exerting an oppositely directed differential pressure on the work device connected to the work ports.

For certain applications, it is desirable to provide a spring-bias against plates 15a, 1512 as shown in Fig. 4, where coil springs 44a provide the respective spring bias. The operation of the servo-valve will be substantially as described above, with the exception that the fluid pressure in the chambers at the outer ends of the spools need not be as great as in the embodiment described in Fig. 1.

It has been found that with the servo-valve construction described above, the need for dither is effectively eliminated. This is due to the fact that there is always movement, however slight, of the valve spools, which movement is effective to overcome static friction between the spools and the inner surface of the various valve guides. The valve has been found to have a frequency response as high as 300 cycles per second, 250 cycles per second being a value that is achieved quite readily.

Should dirt particles in the particles in the fluid system tend to clog up the nozzle clearance between the spool and the armature 109, the spool will tend to move away as the pressure in the outer end of the spool is reduced by the restriction. The clearance between the spool and the armature will be increased permitting dirt to pass through, thus clearing the nozzle.

The invention is not to be restricted to the specific structural details or arrangement of parts herein set forth, as various modifications thereof may be effected without departing from the spirit and scope of this invention.

I claim as my invention:

1. An electric-to-hydraulic conversion device comprising: a valve body having first and second bores therein of constant cross-sectional configuration, eachhaving an open end and a closed end; a fluid inlet port opening into said open ends of said bores; a movable valve member in each of said bores, in sliding fit with said each of said bores, an axial bore in each of said movable valve members extending from one end thereof to the other end thereof, outlet port means in said valve body opening into said bores in said valve body; a radial orifice in each of said movable valve members intersecting the respective bore associated therewith to provide restricted fluid flow from said respective bore to said outlet port means, electrically positioned means pivoted between said bores in said valve body and adapted to be movable relative to said movable valve members so as to provide adjustable orifices for fluid flow into each of said axial bores.

2. A hydraulic servo-valve comprising: a valve body, first and second cavities therein each having an open end opening into a common chamber adapted to be connected to a source of fluid pressure each of said cavities further having a closed end; first and second movable valve spools respectively adapted for reciprocating motion in said first and second cavities; a load port and a drain port opening into each of said cavities in the order named between the open end and the closed end of said each cavity; each of said valve spools having a bore extending between said ends thereof; each of said spools comprising at least a first reduced section, a first enlarged section, a second reduced section and a second enlarged section in the order named between the open end and the closed end of the spool cavity corresponding thereto; each of said second enlarged sections being adapted to block direct fluid communication between the drain port and said closed end of the spool cavity corresponding thereto; said first enlarged section being adapted to block fluid communication between the load port corresponding thereto and the drain port corresponding thereto and permitting fluid communication between said load port corresponding thereto and said common chamber when said spool is within said cavity corresponding thereto greater than a given distance and permitting fluid communication between said load part corresponding thereto and said drain port corresponding thereto and blocking fluid communication between said load port and said common chamber when said spool is within said cavity less than a given distance, an orifice permitting restricted fiuid communication between said bore and said drain port, and means for oppositely varying fluid entry into said bores in said first and second valve spools.

3. A hydraulic servo-valve comprising: first and second valve spools each having an axial bore therethrough; first and second valve cavities each having a closed end and an end opening into a common chamber, respectively adapted to receive said valve spools for reciprocating motion therewithin; first and second load ports in fluid communication with said first and second valve cavities respectively; first and second drain ports in fluid communication with said first and second valve cavities, respectively, between the load port and closed end corresponding thereto; each of said first and second valve spools having a first enlarged section thereon adapted to cut off direct fluid communication between the drain port and closed valve cavity end corresponding thereto; each of said first and second valve spools having a second enlarged section adapted to cut off fluid communication between said common chamber and said load port corresponding thereto when said valve spool is moved toward said common chamber from said central position and to cut ofl fluid communication between the drain port and load port corresponding thereto when said valve spool is moved toward said closed end corresponding thereto from said central position, and an orifice in each of said first and second valve spools adapted to permit restricted fluid flow between the axial bore and drain port corresponding thereto.

4. An electric-to-hydraulic conversion device comprising: a valve body having at least one cavity of regular cross section therein, said cavity having an open end and a closed end, said open end opening into a chamber tit adapted to be put under fluid pressure, a movable valve member within said cavity adapted for longitudinal movement having two collars in sliding fit with said cavity, an axial bore extending longitudinally through said valve member between said open end and said closed end, an orifice between said collars for establishing restricted fluid communication between said bore and an exhaust port in said valve housing, electromagnetically actuated means movable with respect to said axial bore adapted to establish an orifice with said open end to meter fluid flow into said bore so that said valve member will seek a position relative to said ele-ctromagnetically actuated means whereat the fluid pressure exterted against said valve member at the end thereof at said open end of said cavity will equal the pressure including the fluid pressure exerted against said valve member at the other end thereof.

5. An electro-hydraulic actuating device, comprising a casing, a chamber within said casing adapted to be hydraulically connected to a source of fluid pressure, first and second valve cavities opening into said chamber, first and second exhaust ports from said first and second cavities respectively adapted for hydraulic connection to devices to be actuated by fluid pressure, drain port means opening into said first and second cavities, first and second movable valve members in said first and second cavities respectively adapted for reciprocation therein, each valve member having a first collar in sliding fit with the cavity corresponding thereto adapted to block fluid communication between said cavity and said load port corresponding thereto until said each valve member moves a given distance into said corresponding cavity, and to block fluid communication between said load port corresponding thereto and the drain port corresponding thereto unless said valve member is less than said given distance in said corresponding cavity; each valve member having a second collar in sliding fit with the cavity corresponding thereto between the drain port chamber opening and the bottom of the said cavity corresponding thereto, each valve member having a bore extending between the ends thereof and an orifice from said bore to the exterior of said each valve member between the collars thereof to provide restricted fluid flow to said drain, each valve member being spring biased away from the bottom of the cavity corresponding thereto to normally block fluid communication between said chamber and the load port corresponding to said each valve member, and electromagnetically actuated means for adjustably and difierentially restricting fluid flow into said bores.

References Cited in the file of this patent UNITED STATES PATENTS 1,892,565 Browne Dec. 27, 1932 2,526,709 Tait Oct. 24, 1950 2,554,158 Spence May 22, 1951 FOREIGN PATENTS 830,705 Germany 1952 

